Instead of IN we can use ANY with arrays casted to enum array, for example:

create table example_table (
-- 
   enum_field example_enum,
-- 
);

select 
  * 
from 
  example_table
where
  enum_field = any(array['ENUM1', 'ENUM2']::example_enum[]);

Or we can still use 'IN' clause, but first, we should 'unnest' it:

select 
  * 
from 
  example_table t 
where 
  t.enum_field in (select unnest(array['ENUM1', 'ENUM2']::example_enum[]));

Instead of IN we can use ANY with arrays casted to enum array, for example:

create type example_enum as enum (
  'ENUM1', 'ENUM2'
);

create table example_table (
  id integer,
  enum_field example_enum
);

select 
  * 
from 
  example_table t
where
  t.enum_field = any(array['ENUM1', 'ENUM2']::example_enum[]);

Or we can still use 'IN' clause, but first, we should 'unnest' it:

select 
  * 
from 
  example_table t
where
  t.enum_field in (select unnest(array['ENUM1', 'ENUM2']::example_enum[]));

Example: https://www.db-fiddle.com/f/LaUNi42HVuL2WufxQyEiC/0

To use an enum array in the 'IN' clause we should cast the passed array as enum array then 'unnest' it, for example:

Table:

create table example_table (
-- 
   enum_field example_enum,
-- 
);

Query:

select 
  * 
from 
  example_table t 
where 
  t.enum_field in (select unnest(array['ENUM1', 'ENUM2']::example_enum[]));

sqlfiddle

Instead of IN we can use ANY with arrays casted to enum array, for example:

create table example_table (
-- 
   enum_field example_enum,
-- 
);

select 
  * 
from 
  example_table
where
  enum_field = any(array['ENUM1', 'ENUM2']::example_enum[]);

Or we can still use 'IN' clause, but first, we should 'unnest' it:

select 
  * 
from 
  example_table t 
where 
  t.enum_field in (select unnest(array['ENUM1', 'ENUM2']::example_enum[]));